1. Field of the Invention
The present invention relates generally to nitrogen-containing dispersants for lubricating oils obtained by reacting a long chain hydrocarbyl-substituted succinic acid or anhydride with an amine, and lubricating oils incorporating such dispersants. More particularly, the invention is directed to a lubricating oil dispersant having markedly improved compatibility toward fluorohydrocarbon elastomer engine seals, a method for making the dispersant, and lubricating compositions (including additive concentrates) incorporating the dispersant. The dispersant composition of the present invention comprises the reaction product obtained by reacting a long chain hydrocarbyl-substituted succinic acid or anhydride with aminoguanidine or basic salt thereof in a ratio of about 1.4 to about 2.2 moles of aminoguanidine, or basic salt thereof, per equivalent of hydrocarbyl succinic acid or anhydride, at a temperature of from about 155.degree. C. to about 200.degree. C. In its several related embodiments the present invention is further directed to a combination of the above dispersant and a polymeric dispersant-VI improver and/or an alkaline earth phenate detergent.
2. Description of the Prior Art
The presence of water and precursors of sludge in lubricating oils constitutes a very serious problem that is associated with crankcase lubricating oils. There occurs in the lubricating oil various foreign particles, such as dirt, soot, and products of decomposition that result from the breakdown of the lubricating oil. The combination of water and such foreign particles results in the deposition of sludge which has a deleterious effect upon the efficient operation of the engine containing the lubricating oil. In order to prevent the deposition of the sludge, various detergents and dispersants are added to the lubricating oil composition.
While the nitrogen dispersants have been used to prevent sludge, varnish and lacquer deposits in lube oils intended for passenger car engines, it is well known that the alkaline earth metal phenate detergents perform a similar function in diesel engines. High levels of nitrogen dispersant and phenate detergent are now required if a lubricant formulation is to pass the latest passenger car test specifications (SG) as well as the latest diesel engine test specifications (CD or CE). Unfortunately, it is frequently necessary for such formulations to also pass engine tests measuring the compatibility of the lubricant with elastomeric engine seals.
Flexible engine seals are used in assembling internal combustion engines to prevent leakage of lubricants at those points where moving parts, such as crankshafts, extend outside the engine block. Because leakage of the lubricant from the internal combustion crankcase is very undesirable, an important consideration when selecting a dispersant for use in the lubricating oil composition is its compatibility with fluorohydrocarbon crankshaft seals. These seals very often comprise fluorohydrocarbon elastomers which are attacked by the dispersant.
When conventional nitrogen dispersants are present in lubricating compositions at passing SG levels, many such compositions will fail the elastomer seal tests. When phenates, especially calcium phenates, are added to the oil along wit the conventional nitrogen dispersants, elastomer compatibility is worse. The problem of seal compatibility is also worsened if, in addition to the nitrogen dispersant, a nitrogen-containing polymeric dispersant-VI improver is present in the lubricant composition. The nitrogen in dispersant-VI improvers, while particularly effective at controlling engine deposits, is generally quite harmful to elastomer engine seals.
Given the problems outlined above, there is needed a dispersant which is sufficiently passive toward fluorohydrocarbon seals that lubricant formulations containing high levels of the dispersant, to meet SG specifications, can also pass engine seal compatibility tests, especially when the lubricant formulations must also comprise high levels of phenate detergent necessary to meet CD or CE diesel engine specifications, or when the formulations include a nitrogen-containing dispersant-VI improver.
In U.S. Pat. No. 4,379,064, Cengel, et al. discloses the passivation of polyamine dispersants to fluorohydrocarbon engine seal compositions that are employed in internal combustion engines by the mild oxidation of such polyamine dispersants.
In U.S. Pat. Nos. 3,272,746 and 3,341,542, Le Suer, et al. disclose lubricating oil compositions containing acylated nitrogen compounds prepared, for example, by reacting a substituted succinic acid or derivative thereof with a nitrogen-containing compound, such as ammonia, aliphatic amines, aromatic amines, heterocyclic amines, or carboxylic amines. The resulting detergent composition comprises an oil-soluble, acylated nitrogen composition characterized by the presence within its structure of (a) a substantially hydrocarbon-substituted polar group selected from the class consisting of acyl, acylimidoyl, and acyloxy radicals wherein the substantially hydrocarbon substituent contains at least about 50 aliphatic carbon atoms and (b) a nitrogen-containing group characterized by a nitrogen atom attached directly to said relatively polar group. Example 38 of these patents teaches reaction of polyisobutene-substituted succinic anhydride and aminoguanidine bicarbonate at a temperature in the range of 130.degree. C. (266.degree. F.) to 165.degree. C. (329.degree. F.). The resulting product is taught for use as a lubricating oil additive and is said to be an effective dispersant. These patents teach that the mixture of acid-producing compound and the nitrogen-containing reactant is usually heated at a temperature above 80.degree. C. (176.degree. F.), preferably within the range of about 100.degree. C. (212.degree. F.) to about 250.degree. C. (482.degree. F.). The patents disclosed aminoguanidines and other guanidines among a host of possible sources of nitrogen-containing compounds. For example, guanidine, 1,3-diphenylguanidine, and 1,2,3-tributylguanidine are disclosed. These patents, however, do not teach or suggest that the resulting dispersants can comprise triazoles, much less specific temperatures one must employ to obtain a dispersant which is predominantly triazole. There is also no teaching or suggestion in these patents as to the relative compatibility toward engine seals of the many different reaction products disclosed. Thus, apart from the fact that the teachings of the '746 and '542 patents are too broad to anticipate or render obvious the present invention, the patents are not even directed to the problem addressed by the present invention, namely, how to formulate a nitrogen-containing dispersant that provides excellent dispersancy and detergency but is also mild toward engine seals of the fluorohydrocarbon type.
In U.S. Pat. No. 4,491,527, Lange, et al. disclosed ester-heterocycle compositions useful as "lead paint" inhibitors and lubricants, e.g., compositions comprising a major proportion of a pentaerythritol ester of an alkenyl succinic acid in which the alkenyl group contains at least about 30 carbon atoms and a minor proportion of a heterocyclic condensation product of said alkenyl succinic acid derived from a 5-membered ring heterocycle containing at least 2 ring hetero atoms separated by a single carbon atom, at least one of said hetero atoms being nitrogen. The heterocyclic condensation product is characterized by the presence of at least one heterocyclic moiety including a 5- or 6-membered ring which contains at least 2 ring hetero atoms, separated by a single carbon atom. Such ring hetero atoms may be oxygen, sulfur, and nitrogen, with at least one thereof being nitrogen. Most often, the heterocyclic moiety contains a maximum of three hetero atoms and a 5-membered ring, preferably, a triazole or thiadiazole ring, and, most desirably, a 1,2,4,-triazole ring. This patent teaches that aminoguanidine and salts of aminoguanidine, such as aminoguanidine bicarbonate, are examples of acyclic heterocycle precursors which may be reacted with the proper acid or acid derivative group. Like the patents discussed above, Lange '527 is not at all concerned with the problem of seal degradation caused by nitrogen-containing dispersants. Lange '527 does not disclose or suggest the invention presently described.
An object of the present invention is to provide a lubricating oil dispersant composition, as well as an additive concentrate or lubricant composition incorporating such dispersant, in which the nitrogen-containing moieties of the dispersant compound are compatible with fluorohydrocarbon-containing elastomeric engine seals. Other objects will be apparent to those skilled in the art.